Delta-hemoglobin equivalent and granularity index as cell-derived biomarkers for the detection of bacterial infections

Background: Prompt and precise detection of an infection in the blood is of great clinical importance in terms of early therapy initiation and the patient's prognosis. Infection-triggered inflammatory cellular and humoral signal-ing cascades offer great opportunities to redefine standard tests. However, while inexpensive and easy-to-use bio-markers for the detection of infections and the concomitant inflammatory processes exist, they are rarely used in clinical practice. We aimed to investigate the correlation of Granularity Index (GI) and Delta-hemoglobin equiva-lent (Delta-He) as inexpensive and easy-to-use cell-derived infection markers with established acute-phase param-eters in a randomly selected patient. Methods: We analyzed plasma concentrations of the established C-reactive protein (CRP) and procalcitonin (PCT) and leukocyte and thrombocyte counts in blood samples of 1,787 patients undergoing routine laboratory in-flammation diagnostics. We also measured the Granularity Index (GI) and Delta-hemoglobin equivalent (Delta-He) in this cohort between February 2019 and February 2020. Results: Delta-He and GI Index significantly correlated with CRP concentration (AUC 0.72, 95% CI 0.71 - 0.74; p < 0.001 for both analytes) and thrombocyte count (p < 0.001 for both analytes) but not with leukocyte count (AUC 0.54, 95% CI 0.50 - 0.59, p < 0.67). Furthermore, Delta-He significantly correlated with PCT (AUC 0.65, 95% CI 0.63 - 0.68, p < 0.001) while GI Index did not. Additionally, thrombocyte count significantly correlated with CRP (p < 0.001) and with PCT concentrations (p < 0.001). Conclusions: Delta-He and GI are two novel, inexpensive and easy-to-use cell-derived hematological biomarkers with the potential to be used as fully automated and highly standardized parameters. These biomarkers would be available on a 24 hours basis in the routine laboratory for the detection of bacterial infections by measuring a complete blood count (CBC) with differential and reticulocyte counts.